1. Field of the Invention
The present invention relates to a cutting insert and a cutting tool, and particularly, to a cutting insert used in an indexable cutting tool and a cutting tool in which the cutting insert is detachably mounted on a tool body.
2. Description of the Related Art
An example of a cutting insert and a cutting tool is disclosed in WO2008/120186. The cutting insert mounted on a tool body described in WO2008/120186 is formed in a substantially hexagonal plate shape, and is equipped with two same opposing end surfaces and a peripheral surface extending therebetween. In the cutting insert, a cutting edge is formed at the intersection portion or the intersecting ridge portion between the end surface and the peripheral surface. The same cutting portions are formed respectively between three particular corners of each end surface, and each cutting portion includes a major cutting edge and a minor cutting edge. Each of the three particular corners has an internal obtuse angle, which is 102.5° according to the description of WO2008/120186. A major rake surface related to each major cutting edge and a minor rake surface related to each minor cutting edge extend on each end surface. A major flank surface related to each major cutting edge and a minor flank surface related to each minor cutting edge extend on the peripheral surface. The major flank surface extending from the major cutting edge of one end surface is formed to be integral with the minor flank surface extending from the minor cutting edge of the other end surface. In the cutting insert, as a plane located medianly between both the end surfaces in such a manner as to bisect the cutting insert is defined as a median plane, each of the major flank surfaces forms an insert internal obtuse angle to a plane passing through the corresponding major cutting edge and being in parallel to the median plane. On the other hand, each of the minor flank surfaces forms an insert internal acute angle to a plane passing through the corresponding minor cutting edge and being in parallel to the median plane. Such a cutting insert in WO2008/120186 and the cutting tool equipped with this cutting insert are a cutting insert used for a so-called high feeding cutter, and the high feeding cutter. Therefore in the cutting tool of WO2008/120186, one corner different from the corners of the cutting insert mounted to the tool body each having a larger angle, that is, the above particular corners is positioned in the leading end of the cutting tool, and a cutting edge angle at the time of using the cutting tool is small. Referring to the figure of WO2008/120186, the cutting edge angle in the cutting tool is approximately 20°.
In addition, WO2008/120188 discloses a different cutting insert and a different cutting tool. The cutting insert mounted on a tool body described in WO2008/120188 is formed in a substantially pentagonal plate shape, and is equipped with two opposing end surfaces and a peripheral surface extending therebetween. In the cutting insert, as a plane located medianly between both the end surfaces in such a manner as to bisect the cutting insert is defined as a median plane, a cutting region including a cutting edge related to one vertex portion of the pentagon and the periphery is uplifted in such a manner as to separate from the median plane. Therefore the major cutting edge and the minor cutting edge in the same cutting region are each inclined to approximately gradually become closer to the median plane as a distance from the common vertex portion increases. A cutting tool on which the cutting insert of WO2008/120188 is mounted is also a so-called high feeding cutter, and the cutting edge angle at the time of using the cutting tool is small.
The cutting inserts and the cutting tools in WO2008/120186 and WO2008/120188 are devised for so-called high feeding cutters. Therefore even in any of the cutting tools, the cutting edge angle is small and a length of the operative major cutting edge in the rotational axis direction of the rotational cutting tool is very short. Accordingly the cutting inserts and the cutting tools described in WO2008/120186 and WO2008/120188 are inappropriate for deep cutting.
On the other hand, in a face mill as a rotational cutting tool capable of performing plane processing at a cutting edge angle of 45° or more, as a cutting insert having cutting edges in both end surfaces, there is generally used a cutting insert in which an angle between the end surface and the peripheral surface is made substantially as a right angle, that is, a so-called negative type of cutting insert. When this negative type of cutting insert is mounted on the tool body, for ensuring a clearance angle in a tool rotational axis direction (axial direction), the cutting insert is arranged on the tool body in such a manner that a negative rake angle is given in the axial direction as a whole. Therefore for ensuring an axial rake angle as the cutting tool to a positive angle, it is required to provide an uplifted portion on the rake surface of the cutting insert, that is, the end surface. In this way, this cutting insert has the limitation to setting the axial rake angle, and is generally inappropriate for making deep cuts. It should be noted that the cutting insert in WO2008/120188 is a so-called negative type of cutting insert.